Lamp power supply



y 1961 M. J. RELIS 2,983,848

LAMP POWER SUPPLY Filed April 29, 1957 2 Sheets-Sheet 1 POWER HSVJ SUP/4y 54 60- 6 co/vsm/vr a CURRENT 40 II II 1.. -58 SUPPLY INVENTOR.MdTT/IEW J. REL/8 BY A 7' TOR/YE Y May 9, 1961 M. J. RELIS LAMP POWERSUPPLY Filed April 29, 1957 VOLTAGE AT CONTROL GRID 0F I AOUI/M TUBEBEFORE 0.0. UPI/7 0N LAMP O A A 14.0. CURRENT THROUGH LAMP 40. V01. 7/1GE ACROSS LAMP 2 Sheets-Sheet 2 1N VEN TOR. MATTHEWJ REL/6 A 7'7'ORNE Ynited States Patent i LAMP POWER SUPPLY Matthew J. Relis, Bayside, N.Y.,assignor to Burroughs Corporation, Detroit, Mich., a corporation ofMichigan Filed Apr. 29, 1957, Ser. No. 655,615

5 Claims. (Cl. 315-175) This invention relates in general to an arc lamppower supply and more particularly to a power supply that caneconomically initiate and maintain a constant intensity source of light.

Gas discharge tubes which are also referred to as are lamps exhibitparticular starting and operating characteristics which must beconsidered carefully when selecting a power supply to initiate andmaintain operation of the lamp.

For example, a typical mercury arc lamp, when cold, requires a minimumpeak potential of approximately four hundred volts to initiate an arc.Immediately after the lamp starts to conduct the potential across thelamp drops to approximately 30 volts R.M.S. Continued operation of thelamp results in the dissipation of energy in the form of heat, whichincreases the pressure of the gas in the lamp gradually. Due to thisgradual increase in gas pressure within the lamp, the voltage requiredto maintain the arc lamp operating increases gradually until a state ofequilibrium is reached at which time the arc drop across the lamp isapproximately two hundred and fifty volts R.M.S. The time diflrerentialbetween the initiating of an arc in the lamp and the attaining of steadystate conditions is approximately three minutes.

The magnitude of the current that flows through the lamp is determinedby the magnitude of the lamp arc drop and by the impedance of the powersupply. Initially the arc drop is low and therefore the current is rela:tively high. If, however, the electrical power that is supplied to thelamp exceeds the power that is dissipated by the lamp in the form ofheat and light, then the magnitude of the arc drop will increasegradually as already indicated and the current through the lamp willdiminish slowly until a balance of power is established. For properoperation of the lamp the power supply must be designed to deliver ratedpower to the lamp when steady state operating conditions prevail.

The simplest form of power supply for utilization with an arc type oflamp is a source of constant current that has a high internal impedance.Immediately before an arc lamp starts to conduct the high internalpotential of the source of constant current will appear across the lamp.This potential must be of sufficient magnitude to initiate an arc in thelamp. The source of constant current should be designed to feed ratedpower to the lamp after steady state operating conditions prevail. Thusthe design of the power supply is determined by the magnitude of thepotential required to initiate the operation of the lamp, and by themagnitude of the current fed to the lamp during steady state. operation.

An auto transformer will satisfy these conditions. If a step-upautotransformer is wound to present a high secondary winding leakagereactance it will approximate a source .of constant current and willsatisfy the conditions for starting andoperating an arc lamp. The lowvoltage input winding of the autotransformer is connected to a standardone hundred and fifteen volt sixty a 2,3,848 Patented M y 1961 cyclepower line and the high voltage output Winding is connected to the arclamp.

The instantaneous intensity of light generated by an arc lamp isdetermined by the magnitude of the instantaneous power fed to the lamp.Thus, an arc lamp operated from a supply of alternating current willproduce light that varies in intensity with the variations in theinstantaneous magnitude of the applied input power.

In many applications such as photography or photoelectric scanning theintensity of the light produced by an arc lamp must remain absolutelyconstant. Since the intensity of the light from an arc lamp isdetermined by the magnitude of the power fed to the lamp, then aconstant intensity source of light can only be obtained from an arc lampfed .by a lamp power supply that produces a direct current potentialthat is free of ripple.

A direct current power supply that can be utilized to generate arelatively constant intensity source of light consists of a high voltagerectifier coupled to the arc lamp through a series resistor. Therectifier must be capable of supplying the necessary open circuitpotential required to initiate operation of the lamp. The seriesresistor provides the internal impedance required to limit the currentfed to the lamp to its rated value. This type of direct current powersupply is expensive to build and inefiicient to operate. The maximumvolt-amperes supplied by the power supply is determined by multiplyingthe magnitude of the open-circuit potential by the initial current drawnby the lamp. With reference to the Hanovia AH-8 mercury arc lamp, atypical arc lamp, the open circuit potential required for positiveactivation of the lamp is in the order of six hundred volts, while theinitial current drawn by the lamp is approximately eight-tenths of anampere. The initial power drawn is 480 watts. Approximately threeminutes after the arc is initiated, the lamp reaches its steady stateoperating conditions. At this time approximately eighty watts isrequired to operate the lamp and an additional one hundred and twentywatts is dissipated in the series current limiting resistor. Thus, thepower supply must be capable of supplying four hundred and eighty wattsto initiate the operation of the arc lamp although only eighty watts isrequired by the lamp during the major portion of its operating cycle,and then an additional one hundred and twenty watts is wasted in thecurrent limiting resistor.

It is a primary object of this invention to provide an improved powersupply for an arc lamp to generate a constant intensity light free ofripple or fluctuations.

It is another object of this invention to provide an improved powersupply for an arc lamp that is economical to produce and to operate.

It is an additional object of this invention to provide an improvedpower supply for an arc lamp that is reliable in operation regardless oflamp variations or power line potential fluctuations.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the apparatus becomes better understoodby reference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. 1 illustrates the invention in block and schematic tivated totransfer the arc lamp from the source of alternating current to a sourceof direct current without interrupting the operation of the arc lamp.The switching procedure is synchronized to occur after the lamp reachessteady state operating conditions and during the occurrence of thepositive portion of the output signal from the source of alternatingcurrent to prevent interruption of the operation of the lamp. The lightgenerated by the arc lamp is not utilized until after the source ofdirect current has been substituted for the source of alternatingcurrent. The source of alternating current is utilized to initiate theoperation of the lamp, and the source of direct current is utilized toeconomically operate the arc lamp as a source of constant intensitylight.

Referring to Fig. 1, an autotransformer 10 that exhibits a high leakagereactance is utilized as a source of alternating current to initiate theaction of an arc lamp 50. Two input terminals 12 and 14 of theautotransformer 10 are coupled through an on-otf switch 8 to a standard115 volt 60 cycle power line. The output terminals 16 and 18 of theautotransformer 10 are coupled respectively to a stationary contact 22of a relay 20, and to the positive output terminal 60 of a directcurrent bias supply 64. The movable contact 24 of the substitutionswitching means or relay 20 is coupled to a terminal 46 of an arc lamp50, to the control grid of a thyration tube 44 through a resistor 38 anda capacitor 40, and to the anode of the thyratron tube 44 through aresistor 36 and the relay coil 34. The shield grid of the thyratron tube44 is coupled to the positive output terminal 60 of the bias supply 64through an on-olf switch 74, and to the negative output terminal 62 ofthe bias supply 64 through a resistor 68. The stationary contacts 26 and28 of the relay 20 are connected together and to the positive outputterminal 52 of a source of regulated constant current power. Thenegative output terminal 56 of the source of regulated constant currentpower 54 is connected to the terminal 58 of the arc lamp 50, and to thepositive output terminal of the direct current bias supply 64-.

The negative output terminal 62 of the bias supply 64 is coupled to thecontrol grid of the thyratron tube 44 through a resistor 70. The movablecontact 30 of the relay 20 is coupled to the positive output terminal 60of the bias supply 64 through a resistor 66. The source of regulatedconstant current 54 is energized by the standard 115 volt 6O cycle powerline through the on-off switch 8 and the conductors 71 and 72.

In the operation of this invention, the autotransformer 1 is the sourceof alternating current that initiates the action of the arc lamp 50.This transformer has a high leakage reactance which limits the currentthat is initially drawn by the lamp.

When the on-olf switch 8 is closed, the potential that appears acrossthe output terminals 16 and 18 of the transformer 10 is fed throughnormally closed contacts 22 and 24 of the relay 20 to the arc lampInitially, when the source of alternating current is being utilized toinitiate the operation of the lamp, the thyratron tube 44 is notconducting, the relay coil 34 is deenergized, and the contacts of therelay 20 are in the position shown in Fig. 1. Immediately after the lampstarts to conduct, the magnitude of the R.M.S. potential present acrossthe lamp 50 starts to increase while the magnitude of the R.M.S. currentthrough the lamp 50 starts to decrease. This condition exists becausethe arc drop of the lamp increases as the lamp approaches its steadystate operating conditions.

Since the arc lamp 50 functions as a non-linear resistor, the Wave formof the voltage that appears across the arc lamp during the initialtransient period represents a wave that is flattened on top andapproximates a square wave.

Referring in particular to the Hanovia AH-8 type of mercury arc lamp,immediately after the lamp starts to conduct the potential that appearsacross the lamp slowly increases to a steady state value ofapproximately two hundred and eighty volts R.M.S. while the currentthrough the lamp falls to a steady state value of approximately threehundred and fifty milliamperes.

At any instant after the arc lamp has reached its steady state operatingcondition, the point of minimum demand by the arc lamp upon the directcurrent source has been reached, and the source of regulated constantcurrent can be substituted for the source of alternating current.

Referring further to Fig. 1, the resistors 38 and 70 function as avoltage divider to pass a small portion of the potential that appearsacross the arc lamp 50 to the control grid of the thyratron tube 44. Thecapacitor 40, in combination with the resistors 38 and 70 differentiatesthe signal that is fed to the control grid of the thyratron tube 44. Thedirect current bias supply 64 maintains the control grid and shield gridof the thyratron tube 44 at a negative potential to prevent the tubefrom firing when positive half cycles of the alternating potential arepassed through the resistor 36 and the relay coil 34 to the plate of thetube.

When the arc lamp is initially activated the source of regulatedconstant current power 54 must be maintained in its normal operatingcondition.

This is accomplished by connecting a loading resistor 66 across theoutput terminal of the source 54 by means of the relay contacts 28 and30. The loading resistor maintains the source of regulated constantcurrent power in its normal operating mode immediately prior to theswitching operations. If the loading resistor were not present, then thesource of regulated constant current power 54 would not be supplyingcurrent immediately prior to the switching operation and, therefore, thesupply 54 would not be operating as a constant current power supply. Theloading resistor prevents the sudden demand for current which occursduring the switching operation from producing an extreme transientcondition in the source of regulated constant current and the possibleinterruption of the operation of the lamp. The loading resistor ispreset to the largest value that will insure proper switching tominimize the power drawn by it. Approximately three minutes after theon-ofi switch 8 is closed, the potential across the lamp and the currentthrough the lamp stabilize and the lamp is in condition to betransferred from the source of alternating current to the source ofregulated direct current. To accomplish this the bias is removed fromthe shield grid of the thyratron 44 by closing the switch 74, and thethyratron tube fires when the instantaneous magnitude of the positivepotential pulses fed to the control grid is sufiicient to overcome thenegative bias on the control grid. The actuation of the switch 74 can beeither manual or automatic.

The activation of the thyratron tube 44 energizes the relay coil 34 andthe movable contacts 24 and 30 move in a downward direction to transferthe arc lamp 50 from the source of alternating current to the source ofregulated constant current without interrupting the operation of the arclamp. Thus, the thyratron tube functions as an energizing means for therelay. The action of the relay removes the load resistor 66 from theoutput terminals of the source of regulated constant current.

In actual operation of this invention, intermittent closure or chatterof the relay contacts does not occur as an arc is maintained across therelay contacts 22 and 24 during the entire switching procedure. The arepermits a flow of current that is sufficient to sustain operation of thelamp 50. The normally opened contacts 24 and 26, and the source ofregulated constant current hold the relay in its energized condition.The operating time of the relay should not be greater than one-quarterof the period of the supply voltage frequency otherwise it will notoperate before the internal of the autotransformer drops below themagnitude of the lamp potential, which occurs at full conduction, andthe lamp will be extinguished during the switching operation.

To effectively switch the lamp from the source of alternating current tothe source of regulated constant current, the switching operation mustoccur when the alternating current potential across the lamp is substantially at its maximum value.

During switching, as the movable contact arm 24 moves downward, an arcoccurs between the movable contact 24 and the stationary contact 22. Asthe arm continues to move downward, it makes contact with the stationarycontact 26, however, the are between the movable contact 24 and thestationary contact 22 is still present. Thus, immediately after themovable armmoves downward, a conductive path exists between the sourceof alternating current and the source of regulated constant currentthrough the arc across the open contacts and the closed contactsof therelay. At the same time the arc drop across the lamp reaches its maximumpositive value, the lamp is not fully conducting (Fig. 2), and

the differential between the instantaneous arc drop of the lamp and theinstantaneous internal of the autotransformer is relatively small.However, the in ternal E.M.F. of the source of regulated constantcurrent is considerably greater. Therefore, if the movable contact arm24 contacts the stationary contact 26 at this instant then the source ofregulated constant current will assume a substantial portion of the loadrequired by the lamp.

The are across the contacts 22 and 24 persists as long as the internalof the autotransformer exceeds the arc drop of the lamp by an amountequal to the potential drop due to the are that appears across thecontacts. As the internal in the transformer decreases, the arc acrossthe contacts is extinguished and the lamp becomes fully disconnectedfrom the autotransformer, and the constant current supply assumes thefull load.

The operation of switching the lamp from the source of alternatingcurrent to the source of regulated constant current produces a transientcondition in the output signal from the source of regulated constantcurrent. Sufficient time must be allotted for this transient conditionto pass before the autotransformer is disconnected from the switchingoperation, otherwise the lamp may not remain in a conductive state. Thesource of regulated constant current should be adjusted to maintain thesame steady state conditions in the lamp after the switching operationas existed in the lamp prior to the switching operation.

The switching operation can not be effected during the negative portionof the lamp wave form. If this were attempted the positive potentialcurrents supplied by the source of regulated constant current wouldnullify the negative current supplied by the transformer toreduce thecurrent flowing through the lamp to a value below the value needed tosustain operation.

Immediately after the switch 74 is closed, a positive potential pulsesignal appears on the control grid of the thyratron 44 when the lamppotential begins to go positive. However, due to the delay of theoperation of the relay, the relay does not begin to operate untilshortly after the lamp potential passes its positive peak. The circuitdescribed above insures the occurrence of switching at the proper pointin the AC. supply voltage cycle.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A lamp power supply to initiate and produce a source of constantintensity light in an arc lamp comprising a source of continuous lowfrequency alternating current; a high leakage reactance autotransformerfed by said source of continuouslow frequency alternating current toactivate said are lamp until steady state conditions prevail; a sourceof regulated constant 6 current to activate uniformly said arc lamp, arelay to couple said high leakage reactance autotransformer to said arclamp, then couple said source of regulated constant current to said arelamp, and then decouple said high leakage reactance autotransformer fromsaid arc lamp; a load impedance coupled to maintain said source ofregulated constant current operative during the operation of said arclamp by said high leakage reactance autotransformer; a thyratron tubecoupled to energize said relay to effect the transference of the arclamp from the high leakage reactance autotransformer to the source ofregulated constant current; and a diiferentiator network interposedbetween said thyratron tube and said high leakage reactanceautotransformer to initiate energization of said thyratron tube when themagnitude of the signal from the high leakage reactance autotransformeris at a maximum value to insure continuous operation of said arc lamp.

2. A lamp power supply to initiate and produce a source of constantintensity light in an arc lamp comprising a course of continuous lowfrequency alternating current; a high leakage reactance transformer fedby said source of continuous low frequency alternating current toactivate said are lamp until steady state conditions prevail; a sourceof regulated constant current to activate uniformly said arc lamp; arelay to couple said high leakage reactance transformer to said arelamp, then couple said source of regulated constant current to said arelamp, and then decouple said high leakage reactance transformer fromsaid are lamp; a load impedance coupled to maintain said source ofregulated constant current operative during the operation of said arclamp by said high leakage reactance transformer; a thyratron tubecoupled to energize said relay to effect the transference of the arclamp from the high leakage reactance transformer to the source ofregulated constant current; a source or direct current coupled to saidthyratron tube to inhibit conduction of said thyratron tube; adifierentiator network interposed between said thyratron tube and saidhigh leakage reactance transformer, and switch means interposed betweensaid source of direct current and said thyratron tube to disconnect saidsource of direct current from said thyratron tube to permit thethyratron tube to conduct during the occurrence of the maximum positiveportion of the signal from the high leakage reactance transformer toinsure continuous operation of said are lamp.

3. Means to initiate and produce a source of constant intensity light inan arc lamp comprising: a starting power supply including a source ofcontinuous low frequency alternating current; a steady state powersupply including a source of regulated constant current to activateuniformly said are lamp; first switching means coupling said source ofalternating current to said are lamp, said first switching means beingoperative, when actuated, to couple said source of regulated constantcurrent to said arc lamp and to decouple said source of alternatingcurrent from said arc lamp; second switching means operative, whenactuated, to actuate said first switching means to effect thetransference of the arc lamp from the source of alternating current tothe source of regulated constant current; and means controlling theactuation of said second switching means so that it is,

initiated at a positive alternation of the alternating current toprevent interruption of operation of said are lamp at the time of saidtransference.

4. Means to initiate and produce a source of constant intensity light inan arc lamp comprising: .a starting power supply including a source ofcontinuous low frequency alternating current; a steady state powersupply including a source of regulated constant current to activateuniformly said are lamp; switching means to couple said source ofalternating current to said arc lamp, then couple said source ofregulated constant current to said are lamp, and then decouple saidsource of alawar ternating current from said are lamp; a load impedancecoupled across said steady state power supply "to maintain said sourceof regulated constant current operative i p fif a d limp, y s id st inpower supply, said load impedance beingd ecoupled' said Switching meansfrom said source of reg'iilated constaiit current when said startingpower supply'is decoupled from said are lamp; a gas tube coupled toenergize said switching means to effect the transference of the arc lampfrom the low frequency alternating current to the source of regulatedconstant current; and means coupled to said gas tube and to'sfaid arclamp to initiate energization of said gas tube at a positive alternation of the alternating current to prevent interruption of Operation ofsaid are lamp.

Means to initiate and produce a source of constant intensity light inanare lampcompr'isin'g: a starting power supply including a source ofcontinuous low frequency alternating current and a high leakagereactance transformer fed bysaid source of continuous low frequencyalternating current to activate said are lamp until steady stateconditions prevail; a steady state power supply including a source ofregulated constant current to activate uniformly said are lamp; a relayto couple said high leakage reactance transformer "to said are lamp,then couple said source of regulated constant cur rent tosaid are lamp,and then'decouple said higli'leakage rea'ctance transformer from'said'arc lamp; aloa'd i'rnpedanc'coupled across said source of regulatedconstant current to maintain said source of regulated constant currentoperatiyle' during theoperation of said are lamp by said transformer,said load impedance being decoupled from said source of regulatedconstant'current when saidreactance transformer is decoupled from saidare lamp; a gas tube coupled to energize said relay to effect thetransference of the arc lamp from the high leakage reactance transformerto the source of regulated' constant current; and means coupled to saidgas tube and" to'said are lamp to initiate energization of said gas tubeat a positive alternation of the high leakage reactance transformer toprevent interruption of operation of said arc'larnp."

References Cited in the file of this patent

